1. Field of the Invention
The present invention relates generally to a magnetic disk drive, and more particularly to a spindle shaft fixing structure capable of reducing a noise at starting a magnetic disk drive.
2. Description of the Related Art
In recent years, a magnetic disk drive as a kind of external storage device for a computer has been increasingly reduced in size, particularly in thickness, and low power consumption has been required. On the other hand, increasing the recording density of a magnetic disk to increase the capacity has been required, and the number of magnetic disks to be mounted in a magnetic disk drive is increasing. In a magnetic disk drive for a computer, a contact start and stop (CSS) system is generally adopted as the relation between a magnetic head and a magnetic disk. This system is such that while the magnetic disk is in rotation, the magnetic head is kept flying from the magnetic disk at a microscopic height owing to the balance between a flying force applied to the magnetic head by an air flow generated by high-speed rotation of the magnetic disk and an elastic force of a suspension pressing the magnetic head on the magnetic disk.
When the rotation of the magnetic disk is stopped, the magnetic head is moved to a contact zone formed on the magnetic disk and then comes into contact with the magnetic disk in the contact zone. While the magnetic disk is at rest, the magnetic head and the magnetic disk are kept in contact with each other. The magnetic disk is rotationally driven by a spindle motor. The spindle motor includes a spindle shaft fixed to a housing and a spindle hub rotatably mounted on the spindle shaft through a pair of bearings.
A plurality of magnetic disks equally spaced from each other are fixed to the spindle hub by alternately mounting the plural magnetic disks and a plurality of annular spacers on the spindle hub and securing a clamp to the spindle hub by means of screws. A coil is fixed to the spindle shaft, and a yoke and a permanent magnet are fixed to the spindle hub to form a rotor. The rotor is rotatably supported through a pair of ball bearings to the spindle shaft. In the conventional magnetic disk drive, the spindle shaft is fixed at its lower end to a base, and the upper end of the spindle shaft is fixed directly to a cover by a screw. Similarly, an actuator shaft is also fixed at its lower end to the base, and the upper end of the actuator shaft is fixed directly to the cover by a screw.
Since the spindle shaft and the cover are directly connected by the screw in the conventional magnetic disk drive, vibrations generated in the spindle motor are transmitted directly to the cover. As a result, vibrations are induced in the cover, causing an increased noise. Further, in an elastic deformation mode of the motor, the spindle shaft resonates to wave, and the waving of the spindle shaft causes resonance of the cover. Further, each ball bearing for rotatably supporting the spindle hub has a vibration frequency proportional to rotation, and the vibrations in the elastic deformation mode of the motor and the vibrations of ball components of the ball bearing cause resonance at a specific frequency (about 2.7 kHz), resulting in the generation of a grating resonant noise at starting the magnetic disk drive.
On the other hand, the actuator shaft is also connected directly to the cover by the screw. Accordingly, when an actuator for moving the magnetic head is energized to perform a seek operation (swing operation), vibrations of the actuator are transmitted to the cover as in the case of the spindle motor mentioned above, causing a noise due to the vibrations of the cover. In U.S. Pat. No. 5,483,397, a single metal washer having a viscoelastic member preliminarily attached thereto is interposed between a spindle shaft and a cover, and an upper end portion of the spindle shaft is fixed to the cover. According to this fixing structure, the transmission of vibrations of the spindle shaft to the cover can be suppressed. However, if shock is applied to the magnetic disk drive, there is a possibility that the fixing portion may be deformed to cause separation of the viscoelastic member.
It is therefore an object of the present invention to provide a magnetic disk drive which can reduce the noise at starting.
In accordance with an aspect of the present invention, there is provided a magnetic disk drive comprising a base; a shaft fixed to the base; a cover fixed to the base and having a hole at a position corresponding to the shaft; a first washer placed on the cover at a portion around the hole; a second washer for sandwiching the cover at the portion around the hole in cooperation with the first washer; and a screw for securing the first and second washers to the shaft.
Preferably, the first and second washers have elasticity. More preferably, each of the first and second washers has an outer diameter larger than the diameter of the hole, and the screw has a head having a diameter smaller than the diameter of the hole.
In accordance with another aspect of the present invention, there is provided a magnetic disk drive comprising a base; a spindle shaft fixed to the base; a coil mounted on the spindle shaft; a spindle hub rotatably mounted on the spindle shaft; a magnetic disk fixed to the spindle hub and having a plurality of tracks; a permanent magnet fixed to the spindle hub so as to define a gap between the coil and the permanent magnet; a magnetic head for reading/writing information from/to the magnetic disk; an actuator for moving the magnetic head across the tracks of the magnetic disk; a cover fixed to the base and having a hole at a position corresponding to the spindle shaft; a first metal washer placed on the cover at a portion around the hole and having an outer diameter larger than the diameter of the hole; a second metal washer for sandwiching the cover at the portion around the hole in cooperation with the first metal washer, the second metal washer having an outer diameter larger than the diameter of the hole; and a screw for securing the first and second metal washers to the spindle shaft.
Preferably, the magnetic disk drive further comprises a first annular viscoelastic member interposed between the first metal washer and the cover; and a second annular viscoelastic member interposed between the second metal washer and the cover. More preferably, when the screw is not tightened, the first and second metal washers are spaced from each other, whereas when the screw is tightened, the first and second metal washers come into close contact with each other.
In accordance with a further aspect of the present invention, there is provided a magnetic disk drive comprising a base; a spindle shaft fixed to the base; a coil mounted on the spindle shaft; a spindle hub rotatably mounted on the spindle shaft; a magnetic disk fixed to the spindle hub and having a plurality of tracks; a permanent magnet fixed to the spindle hub so as to define a gap between the coil and the permanent magnet; a magnetic head for reading/writing information from/to the magnetic disk; an actuator for moving the magnetic head across the tracks of the magnetic disk, the actuator having an actuator shaft fixed to the base; a cover fixed to the base and having a hole at a position corresponding to the actuator shaft; a first metal washer placed on the cover at a portion around the hole and having an outer diameter larger than the diameter of the hole; a second metal washer for sandwiching the cover at the portion around the hole in cooperation with the first metal washer, the second metal washer having an outer diameter larger than the diameter of the hole; and a screw for securing the first and second metal washers to the actuator shaft.
In accordance with a still further aspect of the present invention, there is provided a magnetic disk drive comprising a base; a spindle shaft fixed to the base; a coil mounted on the spindle shaft; a spindle hub rotatably mounted on the spindle shaft; a magnetic disk fixed to the spindle hub and having a plurality of tracks; a permanent magnet fixed to the spindle hub so as to define a gap between the coil and the permanent magnet; a magnetic head for reading/writing information from/to the magnetic disk; an actuator for moving the magnetic head across the tracks of the magnetic disk, the actuator having an actuator shaft fixed to the base; a cover fixed to the base and having a first hole at a position corresponding to the spindle shaft and a second hole at a position corresponding to the actuator shaft; a first metal washer placed on the cover at a portion around the first hole and having an outer diameter larger than the diameter of the first hole; a second metal washer for sandwiching the cover at the portion around the first hole in cooperation with the first metal washer, the second metal washer having an outer diameter larger than the diameter of the first hole; a first screw for securing the first and second metal washers to the spindle shaft; a third metal washer placed on the cover at a portion around the second hole and having an outer diameter larger than the diameter of the second hole; a fourth metal washer for sandwiching the cover at the portion around the second hole in cooperation with the third metal washer, the fourth metal washer having an outer diameter larger than the diameter of the second hole; and a second screw for securing the third and fourth metal washers to the actuator shaft.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.